1. Technical Field
The present invention relates to a method for controlling an idle stop mode in a hybrid electric vehicle, and more particularly, to a method for controlling an idle stop mode in a hybrid electric vehicle in which when an idle stop mode is triggered in a hybrid electric vehicle, in order to accord final control times of an engine, a motor and a continuously variable transmission (CVT), a hybrid control units transmits an idle stop mode triggering signal for a CVT clutch to a transmission control unit (TCU) in advance so that the CVT clutch can be opened in advance, thereby preventing a shock or shaking of the vehicle.
2. Background Art
A typical hybrid electric vehicle, as shown in FIG. 2, comprises an inverter 10, a DC/DC converter 20, a high voltage battery 30, a hybrid control unit (HCU) 40, a motor control unit (MCU) 50, a battery management system (BMS) 60, an engine control unit (ECU) 70, a TCU 80, a clutch and a CVT 90, an engine 100, and a motor 200. The engine 100 and the motor 200 are serially connected to each other and serve as a power source for driving a vehicle. The clutch and CVT 90 serve to transfer a power. The inverter 10, the DC/DC converter 20, and the high voltage battery 30 serve to drive the engine 100 and the motor 200. The HCU 40, MCU 50, BMS 60, ECU 70, and TCU 80 serve as means for controlling the above-described components and are connected to communicate with each other through controller area network (CAN) communications.
Functions of the components of the hybrid electric vehicle are described below.
The HCU 40 is an upper-level controller which controls an overall operation of a hybrid electric vehicle. The HCU 40 communicates with the MCU 50, which is a sort of a low-level controller, to control torque, speed and power-generation torque of the motor and communicates with the ECU 70, which controls the engine for generating a power for voltage generation as a power source, to perform an engine starting-related relay control operation and a failure diagnosis operation.
The HCU 40 also communicates with the BMS 60, which manages an overall state of a battery by detecting a temperature, a voltage, an electrical current, a state of charge (SOC) of a battery which is a main power source, to control torque and speed of the motor according to the SOC. The HCU 40 also communicates with the TCU 80, which determines and controls a transmission gear ratio according to a vehicle speed and a demand of a driver, to perform a control operation for maintaining a vehicle speed required by a driver.
The HCU 40 monitors information (accelerator or brake) requested by a driver and current states of the MCU, BMS, ECU, and TCU to control an output voltage of the DC/DC converter so that energy can be efficiently distributed according to a vehicle state. Here, the DC/DC converter 20 serves to have a power to be supplied for a vehicle electrical equipment load and a 12V battery to be efficiently charged.
The high voltage battery 30 is an energy source for driving the motor and the DC/DC converter 20 of the hybrid electric vehicle. The BMS 60 which is a controller of the high voltage battery 30 monitors a voltage, an electrical current and a temperature of the high voltage battery 30 to control the SOC (%) of the high voltage battery 30.
The inverter 10 receives energy from the high voltage battery to supply a three-phase alternating current necessary for driving the motor, and the MCU 50 controls the motor under control of the HCU 40.
In connection with control of the DC/DC converter 20, the ECU 70 and the TCU 80 receives an accelerator pedal effort and a brake signal of a driver and provides related information to the HCU 40, which is an upper-level controller, to determine vehicle charging energy.
As an accelerating pedal, i.e., accelerator, a hybrid electric vehicle usually uses an electronic throttle control (ETC) type, and when a driver pushes an accelerating pedal, it is converted into a driver requesting torque form, so that torque suitable for a vehicle speed is determined.
That is, the driver requesting torque is set to a mapping value of a vehicle speed and a detecting value of an accelerating pedal, and operating points of the motor, the generator and the engine are determined according to the determined driver requesting torque.
One of main purposes of such a hybrid electric vehicle is to realize a high efficiency vehicle with a high fuel consumption ratio and an eco-friendly vehicle with high emission performance.
In order to achieve the above purpose, a hybrid electric vehicle employs an idle stop mode. Here, the idle stop mode represents a function for stopping idling of the engine when a vehicle stops. Due to the idle stop mode, unnecessary idling of the engine is prevented, thereby improving a fuel consumption ratio and emission performance.
The power of the engine and the motor is transmitted to a vehicle through a transmission, i.e., CVT. In order to stably trigger the idle stop mode, the clutch, the engine and the motor should be organically controlled.
That is, the engine, motor and CVT should be perfectly accorded if the idle stop mode can be attained without causing a shock or shaking of a vehicle. Particularly, the idle stop mode is greatly affected by an oil temperature of the CVT, a cooling water temperature of the engine, and a deceleration.
In order to trigger the idle stop mode, when HCU 40 transmits the idle stop mode triggering signal to the ECU, the TCU and a full auto temperature control (FATC), the TCU opens the clutch to prevent the power of the engine and the motor from being transmitted to a vehicle, and the ECU turns off an engine to prevent the power of the engine from being transmitted. At this time, the HCU transmits a signal to the MCU to have kill torque to be generated in the motor, so that remaining torque of the engine and the motor is removed, whereby the idle stop mode is completely entered.
However, when the hybrid electric vehicle enters the idle stop mode, the vehicle should decelerate and stop linearly and quietly, but a shaking suddenly occurs, and so a driver does not feel a linear deceleration but alienated. That is, a driver experiences unexpected deceleration feeling (i.e., drag feeling), thereby deteriorating a commodity of a hybrid electric vehicle.
As shown in an operation profile graph of FIG. 4, when the idle stop mode is triggered, motor torque is generated to control the motor until a clutch oil pressure is released, and as the clutch oil pressure does not follow a target pressure, a dip occurs in a P1 speed to affect a vehicle speed, whereby a driver feels alienated due to a shock of a vehicle.
The causes of the above problems are as follows. A vehicle speed for triggering an idle stop mode is determined always at the same vehicle speed, and after an oil pressure of the CVT is opened by a reaction control of the motor, control for triggering the idle stop mode is performed. Therefore, a time when the engine is off and a time when the motor torque is on are not identical, whereby a shock or shaking of a vehicle occurs. In addition, the idle stop mode is triggered without any compensation according to a deceleration, and thus a shock phenomenon gets severe.
Also, a drain time that a clutch oil pressure is fully drained is delayed differently from a target value, thereby causing a shock or a shaking of a vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.